High Quality Content by WIKIPEDIA articles! Bay Area Rapid Transit (BART) is a heavy-rail public rapid-transit system that serves the San Francisco Bay Area. The system is operated by the San Francisco Bay Area Rapid Transit District (SF BART district), a special government agency in California consisting of three counties: Alameda County, Contra Costa County, and the City and County of San Francisco. Serving over 350,000 passengers a day, BART is the fifth largest rapid transit system in the United States in terms of ridership.